Bash doesn't create all files and directories with loop - bash

Question

I'm trying to create a directory with list of directories with list of files.
Could you explain me, why this script doesn't work properly?
createapp() {
local folders=('graphql' 'migrations' 'models' 'tests')
local files=('__init__.py' 'admin.py' 'apps.py' 'views.py')
cd backend/apps
mkdir $COMMAND2
cd $COMMAND2
for folder in $folders
do mkdir $folder && cd $folder
for file in $files
do touch $file && cd ..
done
done
}
It creates a graphql directory, and an __init__.py file in it, but that's all.

Answer 1

There are a few problems:
You aren't iterating over the contents of the array, only the first element.
You are executing cd .. too soon; you want to do that after the loop that creates each file.
for folder in "${folders[#]}"; do
mkdir -p "$folder" &&
cd "$folder" &&
for file in "${files[#]}"; do
touch "$file"
done &&
cd ..
done
There are two ways to simplify this. If you keep the cd command, you only need one call to touch:
for folder in "${folders[#]}"; do
mkdir -p "$folder" && cd "$folder" && touch "${files[#]}" && cd ..
done
Or you can get rid of the cd command, and pass a longer path to touch:
for folder in "${folders[#]}"; do
mkdir -p "$folder" &&
for file in "${files[#]}"; do
touch "$folder/$file"
done
done
or even
for folder in "${folders[#]}"; do
mkdir -p "$folder" &&
touch "${files[#]/#/$folder/}"
done

Answer 2

If you want to get fancy, you can do all of this with zero loops and a combination of bash brace and array expansions:
#!/bin/bash
createapp() {
local folders=('graphql' 'migrations' 'models' 'tests')
local files=('__init__.py' 'admin.py' 'apps.py' 'views.py')
IFS=,
eval mkdir -p "{${folders[*]}}"
eval touch "{${folders[*]}}/{${files[*]}}"
}
Note that the use of eval can be dangerous, but it's pretty limited in this implementation as the two arrays are local and not using user-defined input. If this was zsh, you could embed brace and array expansion without the need for eval